The Contact Patch
by Todd Vosper
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Elden fields many calls from customers and readers. Although I normally handle the
“Contact Patch” duties, here’s a summary of a conversation Elden recently enjoyed:
It’s great to talk to folks that “get it.” Jim Walton is one of those people. He recently
called about a gearing change for his KLR650, and it was immediately obvious that he
understood the problem. What problem you ask? The problem that faces every rider of
a low-powered single: what final gearing to use in each situation, taking into
consideration terrain, road type and conditions, gross vehicular weight, frontal area,
and available power (among other things).
On our DR650’s at Top Gun and MMP, we use final gearing ranging from 14/44 to
15/43 (15/42 is stock). On KLR’s we use 15/43 (stock) to 15/47. People who over-gear
their big singles like the KLR 16/43 crowd are just asking for shorter engine life. The
KLR piston, for instance, is prone to material breakdown between the two top rings.
This is why MMP was the first to carry light, strong, forged pistons; researched and
developed by a quality company. A similar piston was developed for the DR650, also
marketed by MMP. (Todd’s note – in both cases, the firm called on Elden to supply the
cylinder, head, and piston used for product development.) The one in my DR works
great and resulted in less engine vibration, due to being 80+ grams lighter than the
stock piston. You can’t beat lighter AND stronger.
By the way, the diameter and compression are dead stock on both of these forged
pistons. Why not higher compression? Because heat and stress can shorten engine
life, and we can’t get premium gas in many places where we ride.
Top Gun is planning to build a 100,000+ mile KLR650, and a forged piston will be one
of the improvements that will make it possible. More on that later.
Back to Jim. Jim and his son, Chad, have two Japanese KLR650’s (as opposed to
Thailand – lucky guys); their 2000 and 2001 bikes have 11,000 and 15,000 miles
respectively on the clocks. Jim and Chad have been all around the Rockies, to Copper
Canyon (Mexico), to Panama, and are soon to depart for Chile. Jim knows reliability wil
determine how much fun they have. Among the upgrades he plans to make before the
trip is installing the new Kawasaki balancer lever and MMP balancer spring, along with
the Top Gun inspection port. Good luck guys!
Q. Gene Fessenbecker asked “I’ve heard the 2008 KLR only takes 91 Octane
fuel. Is this true?”
A. To set the record straight, the 2008 KLR will still take fuel with an anti-knock rating
of 87 (owner’s manual, page 32). The culprit in this rumor seems to be that the bike is
stamped with “GASOLINE WITH RESEARCH OCTANE NO. (RON) 91 MIN.” RON is the
standard used in most countries outside of the US, Canada, and a few others. In the
US, we use an anti-knock index that is the average of RON and MON – Motor Octane
Number (MON is supposed to be a better measure of how the fuel behaves under
load). MON is normally 8-10 points lower than RON. So the stamp on the bike is
correct, and fuel with an anti-knock index of 87 is still acceptable in the US since it is the
average of 91 RON and 83 MON.
Secondary Air Filter
RCB wrote to us with this info: “hey folks, thanks for that article, and product, re:
Secondary filter on DR. Saved my bacon, apparently. So I have two: 02 and '97, both
low mileage. Checked the '97 today and at first the Secondary A/F looked fine, just a
little discolored, but no breaks in it and appeared serviceable if a bit dirty [3,000 miles
total on that bike]. I put the tip of my little finger in there and barely pushed on that foam
piece and began to crumble. You know the rest.
Great catch! I'll be ordering two of the filters. In the meantime I dug out the 'crosshairs',
thoroughly cleaned everything and made a temporary round foam insert from a foam
piece for an XR650R... it’s too restrictive, but better than nothing at the moment.”
We have been very pleased with the performance of the Top Gun Secondary Air Filter,
both from the standpoint of a more effective and easy to clean filter, and also from the
increased throttle response.
Quick Note About Chain Control
Although it leads to other design advantages as well, one of the primary concerns that
BMW wanted to address on their new 450 Enduro was to co-locate the drive chain axis
and swingarm pivot to eliminate changes in chain length - in other words, reduce chain
slack. You can't eliminate chain slack on your DR650 or KLR650, but maintaining your
DR650 chain rollers or installing a KLR650 Chain Master will definitely help control
excessive slack and reduce wear and tear on your chain and sprockets.
Lastly, we’ve received several questions and seen posts on the Internet about rear
shock absorbers with brittle bump rubber, leaks, and degraded performance after
several years. Here’s the thing folks: you gotta pull ‘em off and service them from time
to time (every couple of years would be a good start). Remember that all of your
suspension components, forks included, do a lot of work every time you ride. The oil is
|Fork oil from a customer's bike.
This is why they need to be
subject to increased pressure, increased
temperature, as well as shearing; and all of
the internal components – especially
consumables like rings and seals – will wear
eventually. Next time you put your bike up
for the winter, make a note to: 1. service
your shock and forks with fresh, quality oil
and replace any parts that are worn, 2.
Install a proper rear spring for your
weight/intended load, and 3. hard-anodize
your shock body and lower fork tubes
(KLR650). For a minimum amount of effort
(and money), most riders will be very happy
with the results.